Stop v5.15.x builds

This change finalizes the v5.15.x builds since official builds from
Proxmox for v5.15.x are already available.

.github/workflows/watch.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: [ubuntu-latest]
     strategy:
       matrix:
-        branch: ['v5.15.x', 'v5.16.x']
+        branch: ['v5.16.x']
     steps:
     - name: Checkout Sources
       uses: actions/checkout@v2

README.md

@@ -3,8 +3,6 @@ Custom Linux kernels for Proxmox VE.
 
 #### Available Versions
 1. Linux 5.16
-2. Linux 5.15
-3. Linux 5.14 **[EOL]**
 
 Older builds are still available at the [Releases](https://github.com/fabianishere/pve-edge-kernel/releases) page.